Q&A: Is it safe to fly through the volcanic ash cloud?

The Civil Aviation Authority has made some alterations to the safety limits for planes flying through clouds of ash. But if you're a holidaymaker whose flight has just been opened up, you're going to want to know: "how safe is it, really?" Wired answers some of the burning questions about the ash cloud.

What are the new safety guidelines?Before the events of April 2010, planes were not allowed to fly through air with any ash in at all. Following the disruption caused by the Icelandic volcano, a limit was set by the Civil Aviation Authority of 2mg of ash per cubic metre of air, which allowed some airspaces to reopen.

However, since midday on 18 May, 2010, the safety limit for planes flying through clouds of ash has been doubled to 4mg, meaning that there can be twice as much ash in one section of air as was previously allowed before a ban is implemented. Any airspace where the density exceeds 4mg is still a no-fly zone.

Why has there been a change of heart?As the disruption has continued, airlines and governments have been sending up test flights to see what the ash actually does to a plane. No one wants a plane to crash, but with chief executives looking alternately at hundreds of grounded planes and then their balance sheets, some had started to question whether the previous ban levels were set at reasonable figures or whether they were over-cautious.

The Civil Aviation Authority has now determined, following that testing and various consultations with airlines, manufacturers of engines and the Air Traffic service that 4mg of ash per cubic metre is safe to fly through without any ill effects to the plane. That figure is still being revised, however, and may extend further in the future.

What is volcanic ash made of?Volcanic ash consists of tiny bits of pulverized rock and glass created in the violence of an eruption, known as tephra. Tephra under 2mm in diameter are classified as ash. Ash is produced in three ways -- either when there’s explosive decompression of a build-up of volcanic gases in a magma chamber, when magma hits water, turns it into steam and then that explosively decompresses, and when there’s thermal contraction of magma hitting water, breaking tiny pieces off.

If the volcano is under a glacier, like in the case of Eyjafjallajökull, the third of those three processes happens. The magma comes up from underground and melts the bottom of the glacier, turning the ice into water. That water chills the lava quickly -- so quickly that it fragments, creating small particles that are then thrown into the air by the force of the eruption.

How do we know where it is?Generally, the amount of ash coming out of a volcano is measured and monitored at the point of eruption, and then computer models are used to track its progress. A traditional rain radar, which most planes are equipped with, won’t detect ash because it's dry, meaning that aircraft have to rely on observations from elsewhere. Happily, radars, lidars and satellites can be tuned to frequencies that can detect these types of particles, so the computer models can be compared to reality.

What can ash do to a plane?There are four different ways ash can attack a plane, and none of them are pleasant. Firstly, ash can clog up the external tubes of the aeroplane – which blocks up vital equipment like the pitot tubes (air speed indicators). Secondly, ash particles are electrically charged, and so can cause severe interference in radio communications with the ground. Thirdly, ash particles impacting the windscreen and lights at high speed will cause scratches. Flying through a high-enough density of ash means that the windscreen gets sandblasted, and impossible to see through, and landing lights can be obscured.

Finally, the engines. During a jet engine’s combustion process, large amounts of air are sucked in. If that air is full of ash, those tiny particles of glass can melt at the high temperatures and fuse onto the blades and other moving parts. If that happens, it can jam the engine, or stop oxygen from reaching the combustion process. Either way, ash goes in, engine goes off.

Has it ever happened before?There are two notable reports of airlines flying through ash clouds and suffering severe damage as a result. In 1982, all four engines of British Airways Flight 9 cut out as it passed through the plume of the Galunggung volcano in Indonesia. The plane was forced to glide for 105 miles before any of the engines were able to restart, but eventually managed to get one working and made a safe landing, albeit with no visibility through the windscreen. It earnt the pilot a Guinness World Record for the longest glide in a non-purpose-built aircraft, and the crew a series of medals.

Seven years later, in 1989, KLM Flight 867 suffered a similar fate when flying between Amsterdam and Tokyo through Alaska. All four engines cut out when the plane passed through the ash cloud from Mount Redoubt, and glass fused onto the turbines. After descending more than 14,000 feet (4,267m), the crew was able to restart the engines and landed the plane safely, however more than $80 million (£54m) of damage was caused to the plane and all four engines had to be replaced.

But the airlines sent up test flights, and none of them crashed, right?Not that we’ve heard, no. In fact, no aeroplane has ever crashed due to ash – just been forced to undergo emergency procedures which won't have been fun for those on board. Some military aircraft continued flying during the airspace closures, but NATO reported finding molten glass in the engines of at least one plane and so RAF training flights were suspended. The Finnish air force also grounded all non-essential training flights after an F-18 returned with damage sufficient to destroy an engine.

What are the airlines saying?FlyBe, a regional airline, said that under the new guidelines it would have only had to cancel 21 flights over the previous weekend due to the ash cloud. Under the old regulations, more than 380 were cancelled and not allowed to fly, so it's clear that the raising of the limits will help out the airlines.

Willie Walsh, the CEO of British Airways, was particularly critical of the previous restrictions, telling the Guardian that blanket bans were "a gross overreaction to a very minor risk", adding: "I am very concerned that we have decisions on opening and closing of airports based on a theoretical model. There was no evidence of ash in the skies over London, yet Heathrow was closed."

What is the Civil Aviation Authority saying?The Civil Aviation Authority is the body responsible for getting airlines, regulators and equipment manufacturers into a room and working out a deal between them.

Andrew Haines, the CEO of the CAA, said about the extension of the limits: "The challenge faced should not be underestimated. Firstly because the standard default procedure for aircraft that encounter ash, to avoid it completely, doesn't work in our congested airspace. Secondly, the world’s top scientists tell us that we must not simply assume the effects of this volcano will be the same as others elsewhere. Its proximity to the UK, the length of time it is continuously erupting and the weather patterns are all exceptional features."

He added: "The answer can only come, therefore, from aircraft and engine manufacturers establishing what level of ash their products can safely tolerate. The manufacturers are co-operating fully and urgently in this task. It's the CAA's job to ensure the public is kept safe by ensuring safety decisions are based on scientific and engineering evidence; we will not listen to those who effectively say 'let's suck it and see."

What is the National Air Traffic Service saying?The Director of the National Air Traffic Service, Ian Hall, was interviewed by the BBC over the restarting of flights, and said: "These are unprecedented circumstances which have required careful monitoring. It’s also given us the opportunity to build up experience -- Airlines and engine manufacturers have been able to build up some additional experience about what happens when aircraft fly in lower ash concentrations. What we’re hopeful for a build-up of experience and evidence that allows those restrictions to be lifted."

Is it possible to build an engine that’s impervious to ash?Ultimately, the answer is no. You can make the windscreen tougher, so it’s less likely to get sandblasted, but it’ll eventually still succumb. You can put filters on the intake channels for air, but they’ll clog up and will need to be replaced. You can fly lower, but that uses rather more fuel, and brings further danger from weather systems that planes normally fly high to avoid.

Even propeller-based planes aren’t immune. They still have engines that need to draw in air and turbine blades that can be coated with molten glass and flame out. Meanwhile, the rest of the plane would be sandblasted by the particles and suffer some nasty erosion. The best thing to do is just avoid a cloud of ash.

So when will the disruption end?No-one really knows. Some scientists claim that the volcano could keep erupting for more than 20 years, potentially paving the way for regular disruption on a scale that hasn’t been seen in a heavily-populated area since commercial flight became the industry it is today.

If the volcano stops erupting, great. If it doesn’t, then the best way forward is more research, careful testing on planes with no passengers in, and finding the right balance between keeping the commercial airlines afloat and passenger safety. With a hefty emphasis on the latter.

Edited by Nate Lanxon

Comments

I think it is dangerous for passengers' safety to let the airlines make the call whether or not they should fly based on the data they are given. This should always be the decision of civil aviation authorities so that it remains unbiased, whether airlines like it or not. I also think it is dangerous to keep increasing over and over again the ash concentration tolerance treshold without knowing more. After all, engines and other plane parts will wear faster and I don't believe planes will be thoroughly inspected after each flight. Every plane that ever crashed was inspected before flying, but may be not as thoroughly as they should have been. So far, they were never any ash cloud fatality but it was due to both luck and pilots' skills. We all know that accidents happen when a series of things go wrong at the same time or in a sequence, not just one. If something else happens at the same time as engines of a plane suck ash, we are in for big trouble. After what we have seen from the tobacco industry, pharmaceutical industry and food industry, it is not far fetched to think that commercial interests are paramount and that passengers' safety comes second. Lufthansa has been reported to ask pilots to use VFR to fly during the ban in April, using their best judgment in order to reach a safe altitude, free of ash. How can a pilot judge if what he sees is ash or a normal cloud ? I'm a capitalist, but I think making money should never mean putting customers' lives at risk.